Process for producing diphenyl



May 18 1937- J. N. cARoTHERs Re. 20,367

n PROCESS- FOR-PRODUQING DIPHENYL original Filed April 7, 192B 1 1 RESIS-rok l l BENZENE STORRQE THNK .Q* 6

y I coNvERToR CONDENSER BENZENE FEED TRN" L P/PEHEHTER y i l coNsrnNT CONDENSER LEVELTHNK y L qnso'METER- 4 HYoRoQEN VENTl FLnsHBolLER Benzene RECEivlNq THNK 9` PUMP 10 REcErvE-R mqn aolLlNQ POINT LIQUID l .1.1. snLL l i 12 QONDENSER.

m H BOILING llNTsRMEom-re 15 cMPouNn i5 somme coMPouNDs DI PHENYL Inventor JN Carni/1ers Bym #ML i l Allorncy;

Reissued May 18, 1937 PATENT' OFFICE PROCESS -FQR PRODUCING DIlI-IENYL John N. Carothers, Anniston, Ala., assignor, by mesne assignments, to Monsanto Chemical Company, St. Louis, Mo., a corporation of Dela- Ware Original No. 1,875,317, dated September 6, 1932, Serial No. 268,096, April 7, 1928. Application vfor-reissue January 18, 1936, Serial No. 59,695

My invention relates to a, method -for the commercial production of diphenyl from benzene, or thc commercially known product, benzol, by the employment 4of heat to raise the temperature of the benzol to that at which diphenyl is formed, and has for its -object the provision of such a process whereby `a high yield of diphenyl may be obtained and a high percentage of diphenyl formed during a single pass of benzene vapors over the heated surface.

A further object of my invention is to provide a process for the commercial production of diphenyl from benzol in which benzol vapors are passed over a heated, surface to raise them to the temperature at which diphenyl is formed,

and wherein objectionable deposits of tar and carbon on the heated surface are practically eliminated.

A' still further object of my invention is to provide a process of the character designated for the commercial production of diphenyl from ben'zol, wherein the unreacted benzolat each pass over the heated surface is recovered and re-treated until it is all reacted upon.

Heretofore, so far as I am aware, diphenyl has -only been produced in small quantities in achemical laboratory. Various methods of di phenyl preparation have been suggested, such as suspending electric heating coils in a flask containing liquid benzene and benzene vapors, or by passing benzene vapor through an externally heated tube. Diphenyl has also been produced by the preparation from solution, such as by adding copper to a solution of diazobenzene sulphate in alcohol, or byiheating monobrombenzene or monochlorbenzene with sodium. In such instances where benzene vapors were heated, the rate of flow of the vapors was uncontrolled, and the heating regulation likewise was uncontrolled.

In my investigations of the preparation of diphenyl from benzene, in which the vapors are passed through a hot tube, I have encountered all the difliculties, reported by previous inv vestigators, as-regards stopping of the tube with carbon, and the formation of tarry bodies. In such references as I have noted, frequent mention is made of the formation of tar and carbon, and

the necessity of frequently cleaning out the tubes when benzene vapors are passed through heated tubes. I have observed that under certain conditions tar is formed and carbon is deposited,

Claims. (Cl. 260-168) osition of carbon, and of'lowering the quantity of tar or other high boiling compounds which are formed, until their presence is neither an objection to the continuous operation of the process, nor a source of great loss of benzene.

By the method of operation which I employ, I am enabled to control the various factors which I have found it is necessary to have under control, and as a. result of this control I am enabled to carry on a commercial operation of this process f and obtain a satisfactory yield of diphenyl from the benzene. By satisfactory yield, I mean vat least 8% diphenyl in the total condensate after one pass.

Although external means of heating may be applied, and satisfactory results obtained, I have found internal heating, i. e. heating the gas stream by means of metallic resistors with electric current to be more satisfactory. It is obvious that internal heating may be accomplished by induction, instead of by resistance. Further I have found that metallic resistors, rather than non-metallic resistors, are better suited for this purpose. While non-metallic resistors are satisfactory for short periods, the electrical resistance drops very rapidly, and in a short time, suoli nonmetallic resistors as have been tested are unsatisfactory because of this change of resistance. Although other metals may be used as a metallic resistor, I have found that nichrome is very satis factory. The heating surface may be arranged as desired, according to the form of the material used.

vwith the heating element which raises the temperature of the vapors to the reaction tempera- .ture at which vdiphenyl is formed. I have found that if the vapors may be quickly raised to the optimum Y temperature at which diphenyl is formed, these depositions of tar and carbon do not occur to an extent which is objectionable to the operation Aof the process. In order to minimize the formation of tar and carbon, I have found that if the vapors be rst raised to the then suddenly subjected to asurface capable of quickly raising-the temperature of the vapors highest temperature permissible, withoutA the formation of appreciable quantities of diphenyl, and

to that at which diphenyl is formed, the time element during which the vapors are in contact with the highly heated surface is greatly rey duced and no objectionable deposits of tar and carbon are formed on the highly heated surface. By this method I am enabled to maintain a re1a tively high velocity over the most highly heated surface so that the vapors pass thereoverso quickly that no deposits are formed. Should tarry compounds be formed,v the fact that they are forming may be observed by an increase in the flow of hydrogen and other uncondensed gases from the gas outlet of the reaction system.

In order to obtain an increased yield of diphenyl, I have found that, immediately the vapors have reached the reaction temperature,

they should be quickly cooled to a temperature considerably Abelow that at which the reaction occurs. The preheating of the vapors followed *by the passing of the vapors over a highly heated element at a relativelyhigh velocity to produce the reaction is of material aid in bringing about the quick cooling feature of my process. This, for the reason that at the relatively high velocity the vapors are immediately subjected to a cooling processin a condenser which should be located as near as possible to the converter in which the reaction occurs. Y

While I do not know the exact extent to which water may be present in commercially pure benzol, without causing trouble in the formation of carbon, nevertheless, I have found water an objection if it is present in such quantities as to separate from the benzol. In view of this observed fact that carbon forms more readily when water is present, than when dry benzol is used, I prefer using water free benzol.

While benzol may be used which is of a grade designated as 90% commercia I have found that the use of this grade of benzol is not satisfactory where it is sought to obtain diphenyl alone, because of the wide boiling range of the product; and as a result of the presence of other compounds than benzene, lower yields of diphenyl are obtained. Also difficulties are encountered in separating the diphenyl from reaction products of these other compounds.

Benzol 'designated at 90% commercial" contains certain percentages of other aromatic hydrocarbons, especially toluene and xylene. These hydrocarbons, along with the benzene, when treated in accordance with my improved process, produce complex di-aryl compounds which' are the other compounds referred to above. For certain purposes, the complex mixture obtained by treating the benzol designated as 90% commercial in my improved process is `superior to pure diphenyl. On the other'hand, when diphenyl with a minimum of the complex di-aryl compounds it is to be produced, itl is preferable to use a commercial grade of benzol, designated as commercially pure. This grade of benzol is of sufcient purity and boils within a 2 C. range, which range includes the true boiling point of benzene. v

In order, that my process may be more readily understood, reference will be had to the accompanyingdiagrammatic drawing outlining the steps thereof. Liquid benzol is fed from a constant level tank 3 into a flash boiler 4, where the benzol is vaporized and passes to a preheater 5 where it is preheated and then passed into a converter 5a, which isprovided with means for heating the vapors to the temperature neces- A the vapors.

sary for the formation of diphenyl according to the following equation:

The preheater may be of any approved type and may gradually or quickly raise the temperature of the vapors to the highest point permissible at which no appreciable reactions occur. I have found that a temperature of from 600 to 650 C., is the optimum temperature for practical purposes. Upon leaving the preheater, the vapors pass, at a relatively high velocity, immediately into 'the converter where they come in contact with a heated surface, which may comprise an electrically heated screen or other suitable surface maintained at a temperature of from 750 to 800 C., the optimum temperature at which di ,phenyl is formed. The vapors'are here raised to a temperature substantially equal to that of the heated surface.Y i v Inasmuch as the vapors, before passing over this surface, have already vbeen raised to a temperature of from 600 to 650 C., there is added only a relatively small amount of heat to 'I'his being the case, a relatively. high velocity of the vapors may be maintained across the heated surface, thus minimizing the occurrence of side reactions and deposits of tar andA carbon.

From the converter 5a the mixed vapors of benzol, diphenyl, di-aryl compounds and hydrogen pass into condenser 6, which is provided with regulated means for quickly cooling the vapors sufficiently to condense the diphenyl and such other compounds as are formed when the benzol vapors are heated. 'I'he diphenyl and other compounds together with some benzol are drawn off into a receiver III, from which it flows into a still I I, from whence separation is effected by a condenser` I2, in which the fractions are separated into high boiling compounds, collected in a tank I5, the intermediate boiling compounds into a tank I4; and the diphenyl into a tank I3. The benzol condensed with the diphenyl in condenser 6 is recondense'd in the condenser I2 and p asses to thereceiving tank 8. The diphenyl and di-aryl compounds are then ready for use in whatever form is desired.

In order to make the process a cyclic operation, the benzol vapors and hydrogen from the condenser 6 pass into a condenser 1, where liquid benzol is collected and ows into a receiving tank 8, whilethe hydrogen is vented through a lgasometer I 6. 'The liquid benzol is returned by a pump 9 through benzol tank 2 to the constant level tank 3, and thence again through the cycle. As the benzol is converted according to the process described, additional benzol is admitted into the system from storage tank I.

While I havedescribed my invention in but one form, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various changes and modifications, without departing from the spirit thereof, and I deslre,`

1. 'I 'he herein described process forfthe production of diphenyl from benzol which comprises raising thetemperature of a stream of benzol vapors in a preheating step until substantially conversion step abruptly raising the preheated vapors in the stream to the optimum temperature range for conversion to diphenyl, and as soon as said vapors have attained Ysaid optimum tem- -raising the temperature of a stream of benzol vapors in a preheating step until the stream is uniformly at a temperature where an appreciable conversion to diphenyl begins. then in a conversion step' abruptly raising the thus preheated vapors in the stream to the optimum temperature range for the conversion to diphenyl. and as soon as said vapors have attained sai-d optimum temperature range, abruptly chilling them to a temperature below the diphenyl forming temperature. thevapors having their stream ow disturbed and accelerated in their passage through the conversion step. y

3. The herein described process for the `production of diphenyl from benzol which comprises raising the temperature of a streamof benzol vapors in apreheating step until the vapors are uniformly at a temperature below but near that at which an appreciable conversion to diphenyl` begins, and then in a conversion step suddenly raising the preheated vapors in the stream to the optimum temperature range for the diphenyl reaction, and as soon as said vapors have attained said optimum temperature range, suddenly chilling them below the diphenyl forming temperature, the vapor stream having a relatively accelerated motion through the conversion step, the raise in temperature in the conversion step being accomplished by heat interchange with elements having a temperature within the optimum conversion temperature range.

4. The herein described process for the production of diphenyl from benzol which comprises raising the temperature of a stream of benzol vapors in a preheating step until the vapors are uniformly at a temperature below but near that at which an appreciable diphenyl reaction begins. then in a conversion step abruptly raising the preheated vapors in said stream to the optimum temperature range for the conversion to diphenyl. and as soon as said vapors have attained said optimum temperature range, abruptly chilling them to a temperature below the diphenyl forming temperature, the vapor stream having a relatively accelerated motion through the conversion step, the raise in temperature for the conversion step being accomplished by heat interchange with elements having a` temperature within the said optimum conversion temperature range which are interposed in the path of the vapors to break up their stream ow in the conversion step.

5. The process of producing diphenyl which comprises preheating a stream of benzol vapors by heatexchange with heating elements having a maximum temperature but below that at which substantial quantities of diphenyl' are formed until said vapors are uniformly near the maximum temperature of said elements, then passing the thus preheated vapor stream into contact withheating means' having'a temperature within the optimum temperature range for the conversion of benzol to diphenyl and so interposed in the path of the vapor stream as to disturb and cause an acceleration of its flow and to uniformly heat it while in Contact with said heating means, and chilling said vapors to a temperature substantially below that at which diphenyl is formed as soon as they have attained a uniform temperaturc near-that of said heating means.

6. The process of producing diphenyl which comprises preheating a stream of benzol vapors by heat exchange with heating elements having a maximum temperature of from 600 C. to 650 C.

until said vapors are uniformly near the temperature of said elements, then passing the thus preheated vaporstream into contact with heating means having a temperature of from 700 C. to to 800 C. and so interposed in the path of the vapor stream as to disturb and cause an acceleration of its flow and to uniformly heat it while in contact with said heating means, and abruptly chilling said vapors to a temperature substantially below 700 C. as soon as they have atta-ined a uniform temperature approaching that of said heating means.

"Lr In the process of producing diphenyl by the pyrolysis of benzol inwhich the benzol vapors are uniformly heated to a temperature of from '700 C. to 800 C. and then cooled to a temperature substantially below 700 C., the improvement which comprises shortening the period during which the vapors are at diphenyl forming temperature by subjecting the vapors to the cooling step as soon as they have attained a temperature of from '700 C. to 800 C 8. In the process of making diphenyl b v heating benzol vapors to diphenyl forming temperatures and then cooling them, the improvement which comprises shortening the period during which the vapors are at diphenyl forming temperatures by rst uniformly preheating the vapors to a temperature below but near diphenyl form-` ing temperature, then abruptly and uniformly heating to raise them to rapid diphenyl forming temperature, and subjecting the vapors to cooling below diphenyl forming temperature as soon as they attain rapid diphenyl forming temperature.

9. The process of producing diphenyl whichr extent that would interfere with the continuous operation of the process.

10. The process of producing diphenylwhich comprises preheating a stream of benzol vapors until substantially all the stream is uniformly within a temperature range of from 600 C. to 650 C. by heat interchange with elements heated to a temperature within said range. and then terfere with the continuous operation p f the perature near that of the heating means. I

11. The process of producing diphenyl which -comprises preheating a stream of benzol vapors bypheat interchange with elements heated to a temperature range of from 600 4C. to 650 C. until the temperature of said stream of vapors is uniform and near that of the heating elements, then passing said vapor stream thus preheated into contact with a heating means heated to a temperature range of from '700 C. to 800 C. and having a heating surface such as abruptly to heat the vapors to a uniform temperature near that of the heating elements and form diphenyl, causing said stream to iiow while in contact with said heating means at such a velocity that side reactions to any appreciable extent are prevented, and abruptly cooling the vapors to a temperature substantially below '700 C. as soon as they attain a temperature near that of `said heating means.

l2. I-n the process of making diphenyl by heatlng benzol vapors to diphenyl Aforming temperaturesl and then cooling them, the improvement which comprises shortening the period vduring which the vapors are in contact with heating elements at diphenyl forming texriperatures4 by first preheating the vapors to a uniform temperature of from 600 C. to 650 C. by contact with.

to a uniform temperatureof from '700 C. to 800v C., and subjecting the vapors to cooling as soon as they attain a temperature of from '700 C. to

13. Theprocess of producing diphenyl which comprises raising the temperature of benzol vapors to a uniform temperature at which benzol begins to pyrolize, then in a conversion step abruptly raising the temperature of the vapors to a uniform temperature within the optimum range for the-substantial pyrolysis thereof, and as soon as the vapors attain said optimum temperature then chilling the vapors to a tempera- `ture below pyrolysis temperature.

14. A process vof producing diphenyl which comprises heating benzol vapors to a` uniform temperature within the optimum range forthe formation of diphenyl, and chilling the vapors to a .temperature below diphenyl .formingtemperature as soon as said vapors attain. diphenyl fo-rming temperature and before the formation lof l; 4tarand carbon begins to an extent -that would interfere with the continuity of the process.

.15. In the process. of producing diphenyl by the pyrolysis of benzol in which the benzolvapors are heated to diphenyl forming temperatures and then cooled .to a temperature below diphenylforming temperature, the improvement which comprises heating the vapors to a uniform temperature at which diphenyl is formed and shortening the period during whichthe vapors are at said .temperature by subjecting them to the cooling step as soon as they have attained diphenyl forming temperature.

JOHN N. CAROTHERS.

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